JPH07315969A - Two-layer high temperature coating provided on ceramic base material and method for forming it - Google Patents

Abstract

PURPOSE: To obtain a two-layer high temp. coating excellent in practical high thermochemical stability and high thermal shock resistance and exhibiting a stable phase and low shrinkage by disposing a barrier layer having a specified contents of constituents and a top coat layer on a porous ceramic substrate.

CONSTITUTION: Quartz glass is pulverized and sieved and 95 pts.wt. quartz glass is blended with 5 pts.wt. SiB₄, diluted with distilled water in a weight ratio of 1:1 and sprayed on the surface of a fibrous ceramic material subjected to dust removal pretreatment. After drying in an oven, the resultant barrier layer (primer layer) is calcined at 1,120°C for about 15 min. Glass consisting of 95 pts.wt. high silica glass and 5 pts.wt. SiB₄ is then pulverized, mixed, dried and calcined at l,250°C to apply a cooled emissivity glaze layer (top coat) on the barrier layer. The barrier layer is thus densified and the objective high temp. coating having 70-140 μm thickness and a high density of 0.5 g/cm³ is obtd.

COPYRIGHT: (C)1995,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to materials that protect ceramic substrates, especially porous ceramic substrates, from erosion and chemical and mechanical failure, and more particularly to coatings.

[0002]

Refractory oxide fibrous ceramic materials that function at high temperatures are widely used. The conditions under which these materials are used are required to have high heat resistance, erosion resistance, thermochemical stability and phase stability for the protective coating.

Currently, a full range of erosion resistant coatings used at temperatures below 1260 ° C. are known. Two-layer coatings are known which comprise a barrier layer and a glaze layer (see US Pat. No. 3,953,646). This barrier layer is formed by the deposition of fused silica having a solids content of about 80-90% by weight. The coating is
It is applied to the substrate by spraying. The barrier layer is about 930
~ Baked at a temperature of about 1370 ° C. A metallic layer composed of high silica glass, borosilicate glass and a radiation activator is applied to the barrier layer. The radiation layer is silicon carbide,
Chromium oxide, cobalt oxide, nickel oxide, nickel-
It is selected from the group consisting of chromium spinel, silicon nitride and calcined mixed oxides of iron, chromium and / or nickel. High silica glass (Corning Glass N)
o. 7913) contains 94% by weight or more of SiO ₂ . Borosilicate glass weight composition (Corning G
lass No. 7740) is SiO ₂ 70-87.
_{%, B 2 O 3 10~20%} , Na 2 O2~5% and Al
₂ O ₃ 1 to 5%.

The high silica glass component and the borosilicate glass component are used in a weight ratio of about 3: 1 to about 19: 1. The glass components (high silica glass and borosilicate glass) and the emissive agent are used in a weight ratio of 50: 1 to about 4: 1. An aqueous slurry containing from about 10 to about 90% by weight of the galenic paint is fired in the temperature range of 930 to about 1370 ° C.

A silica layer and a high silica glass component selected from the group consisting of silicon carbide, nickel oxide, chromium oxide, cobalt oxide, nickel-chromium spinel, silicon nitride and calcined mixed oxides of iron, chromium and cobalt. An emissive agent comprising a high silica glass: the emissive agent in a weight ratio of about 50: 1 to about 4: 1;
A silica thermal insulation three component coating comprising a high silica glass and a borosilicate glass and an overglaze layer composed of a high silica glass: borosilicate glass weight ratio of about 3: 1 to about 19: 1 is known in the art. (See US Pat. No. 3,955,034).
The coating is fired in the temperature range of 930 to about 1370 ° C. These coatings have insufficient thermal shock resistance and thermal radiation stability, and shrinkage occurs.

To overcome these problems, a compound selected from the group consisting of silicon tetraboride, silicon hexaboride, other boron suicides, boron and mixtures thereof.
A one-layer coating made by reacting a high silica porous borosilicate glass with a reactive glass frit consisting of boron oxide has been proposed (US Pat.
093,771). A thin layer of borosilicate glass is formed on the fine particles of high silica glass to improve the sinterability of the coating without substantially increasing the coefficient of thermal expansion.

Reactive glass frits have a boron oxide content of about 2
Advantageously, -10 parts by weight and 100 parts by weight of highly silica porous borosilicate glass such as Vycon® 7930 glass are prepared. Vycon® 7930 high silica borosilicate glass has a porosity of about 28%. Boron oxide, deionized water 200-4
Dissolves in 00 parts by weight. The mixture is stirred at about 95 ° C and then dried at a temperature of 75-95 ° C for up to 24 hours.
The glass frit obtained is dispersed, sieved and 1150
Bake at ℃ for 1 hour. The resulting calcined composite is ground to a powder and screened.

A typical composition is 5.5% by weight of boron oxide.
97.5% by weight of a reactive glass frit containing 5% by weight of silicon tetraboride compound consisting of 63 ± 3% by weight of silicon, 36 ± 3% by weight of boron and less than 0.2% by weight of magnesium. Is. The coating slurry comprises fine particles of reactive glass frit and silicon tetraboride, a carrier such as ethanol and a preliminary binder such as methylcellulose, and solid components 35 to 50.
It is prepared by blending in a weight percentage. The mixture of coating components is milled with alumina balls in an alumina ball mill for 3-12 hours. This coating solution is applied by spraying. The coated sample is dried in the temperature range of 20 to about 70 ° C. for 2 to 5 hours. After drying, the coated sample is polished in an oven at 1215 ° C. for 1.5 hours. The resulting coating has an emissivity of about 0.90 to 0.93 at temperatures from ambient to above 1260 ° C. The coefficient of thermal expansion is
It is 1.1 * 10 <^-6> K < ^{-1 >} .

High performance, low density coatings for protection of aluminosilica porous materials with operating temperatures below 1300 ° C. are also known. The coating composition contained 77.5% by weight reactive glass frit, 2.5% by weight silicon tetraboride, and 20% by weight molybdenum disilicide.
This coating is processed at 1230 ° C. for 1.5 hours to form on a substrate (Advanced Porous).
Coating for low density
Ceramic Insulation Material
als, J .; Amer. Ceram. Soc. 72, No. 6, 1003-1010, 1989). The use of high silica borosilicate glass with an active surface in the coating composition reduces thermochemical and phase stability. The phase transition in the coating is associated with the formation of α-cristobalite, which causes the coating to crack.

[0010]

The present invention provides a high temperature coating on a ceramic substrate that does not have the disadvantages of prior art coatings. The coating according to the invention exhibits in fact a high thermochemical stability, a high thermal shock resistance, a very stable phase and a low shrinkage.

[0011]

SUMMARY OF THE INVENTION The present invention is a high temperature coating provided on a ceramic substrate, particularly a porous ceramic substrate, said coating comprising quartz glass and S.
A barrier (primer) layer containing silicon tetraboride having an iB ₄ content of more than 96% by weight, a high-silica glass, and a radioactivity enhancer containing silicon tetraboride having an SiB ₄ content of more than 96% by weight. And a (topcoat) layer, the layers having the following weight composition: Barrier layer: - four silicon boride (SiB ₄ content: greater than 96% by weight) 0.1 to 10%; - quartz glass: 90 to 99.9%; emissivity Yu drug layer: - four silicon boride ( SiB ₄ content:> 96% by weight): 1.5-5.0% -high silica glass: 95-98.5%.

The ceramic substrate is Al ₂ O ₃ , Zr.
It is made of a ceramic material that generally comprises one or more compounds selected from the group consisting of O ₂ , SiO ₂ , SiC and Si ₃ N ₄ . Its density is generally 10
It exceeds 0 kg / m ³ (0.1 g / cm ³ ).

In the coating, the content of silicon tetraboride particles having a size of less than 5 μm is preferably 70 to 80% by weight of the silicon tetraboride, and the silica glass SiO ₂ content is preferably 99.96% by weight. Further, the high silica glass has a weight ratio of SiO ₂ 94 to 96% and B ₂ O ₃ 3.5 to 6
%, Al ₂ O ₃ 0.1-0.5% and Na ₂ O 0.1-
Advantageously, it contains 0.5%.

Due to the thermochemical properties of high silica glass due to its specific composition, in particular silicon, aluminum and sodium oxide, its high purity and its specific dispersibility, the amorphous (glass) component of the coating and the ceramic polycrystals. The desired chemistry with the (silicon tetraboride) component is ensured. As a result, firing of the ceramic substrate with the coating causes curing of the reactive emissivity agent layer. This curing can substantially reduce shrinkage of the ceramic substrate, increase thermal shock resistance and increase the thermal stability of the coating to stabilize thermochemistry.

The presence of greater than 98.5% by weight of high silica glass and less than 1.5% by weight of silicon tetraboride in the emissivity layer increases the softening temperature of the coating, resulting in phase stability and radiation. Noh is reduced. If this layer contains less than 95% by weight of high silica glass and more than 5% by weight of silicon tetraboride, heat resistance and thermochemical stability will be insufficient.

If the content of silicon tetraboride particles having a size of less than 5 μm exceeds 80% by weight, the penetration into the porous ceramic substrate is substantially increased and the porous ceramic substrate shrinks. On the other hand, when the content of particles of this kind is less than 70% by weight, silicon tetraboride is non-uniformly localized distributed in the glass matrix. As a result, the stress on the coating increases and the thermal shock resistance decreases.

The temperature and dispersion of silicon tetraboride is controlled. When the silica glass content of the barrier layer exceeds 99.9% by weight, the density of the interface between the barrier layer and the base material is too low and the adhesiveness between the coating and the base material is reduced, resulting in the permeability of the radiation layer. And contraction occurs. Further, if the silica glass content is less than 90% by weight, the density of the barrier layer is substantially increased and the impregnation with the slurry composition for forming the emissivity agent layer is not uniform. A crack develops in the Nouyu drug layer.

The use of high silica borosilicate glass with an active surface in the coating composition reduces its thermochemical and phase stability. The phase transition in the coating is associated with the formation of α-cristobalite, which causes the coating to crack.

When the coating penetrates the porous substrate,
High adhesiveness is given. Thickness 70-140 μm, density 5
A densified layer that is less than or equal to 00 kg / m ³ (0.5 g / cm ³ ) is generally formed on the substrate. This coating has a pressure of 0.8 × 10 ^{5 to} 1.1 × 10 ⁵ Pa (0.
It is advantageous to apply with compressed air (8-1.1 atm). The disperse phase (coating powder): dispersion medium (preferably distilled water) weight ratio is 1: 1 to 1: 5. At high dispersion medium contents, especially at high water contents, the chemical composition of the coating becomes non-uniform. The low water content reduces the adhesion between the coating and the substrate. The coating is applied, for example, to the surface of a ceramic substrate that has been pretreated to degrease the felt forming the substrate to improve adhesion.

The barrier (primer) layer is heated to a temperature of 1100.
Calcination is performed at ˜1150 ° C. for 10 to 20 minutes, and the emissivity agent layer (top coat layer) is heated at a temperature of 1250 to 1300 ° C.
Firing for 0-20 minutes can reduce material shrinkage. The shrinkage of the coating material occurs when the firing temperature exceeds 1300 ° C. and the firing time exceeds 20 minutes, while the radiation capacity decreases at the firing temperature and the firing time below the above values.

The invention, according to another aspect, is a method of forming a ceramic substrate, in particular a porous ceramic substrate, having a coating as described above, said method comprising: -silicon tetraboride (SiB ₄ content). Powder of 90% to more than 96% by weight) and 90 to 99.9% by weight of quartz glass in a miscible dispersion medium, preferably distilled water, in a powder to liquid weight ratio of 1: 1 to 1. : Preparing the first slurry added in step 5; -applying the first slurry by pressure spraying onto a pretreated ceramic substrate to be coated, -the layer thus obtained Dry it 1100-1
A step of baking at a temperature of 150 ° C. for 10 to 20 minutes to obtain a barrier layer, silicon tetraboride (SiB ₄ content exceeds 96% by weight) 1.5 to 5.0% by weight, and high silica glass 95 to 9
Preparing a second slurry in which a powder consisting of 8.5% by weight is added to a miscible dispersion medium, preferably distilled water, in a powder: liquid weight ratio of 1: 1 to 1: 5; Is applied to the barrier layer formed in the preceding step by pressure spraying, and-the layer thus obtained is dried and it is 1250 to 1
And a step of calcination at a temperature of 300 ° C. for 10 to 20 minutes to obtain a radiation-stimulating agent layer, the method being provided.

[0022]

EXAMPLES The following examples are intended to illustrate the invention and to explain it in more detail. Example 1: A coating was prepared using the slurry coating-firing method. First, a barrier layer (primer layer) was created. The quartz glass was finely pulverized with an alumina ball mill to obtain a powder having a specific surface area of 0.6 to ¹ m ² / g, which was sieved. 95 parts by weight of quartz glass and 5 parts by weight of silicon tetraboride occupying 70% by weight of particles having a size of less than 5 μm were blended in a polyethylene container for 25 hours. The powder was weighed, diluted with distilled water at a weight ratio of 1: 1 and air pressure was applied to the surface of the dust-free pretreated fibrous ceramic material at 10 ⁵ Pa.
It was applied by spraying (1 atm). This gives a thickness of 10
A 0 μm densification layer was applied. The sample was dried in air for 30 minutes and in an oven at 80 ° C. for 30 minutes. Next, a barrier layer (primer layer) is applied at 1120 ° C. for 15
Bake for minutes.

Next, a cold radiation function medicine layer (top coat)
Was applied to the barrier layer. The emissivity agent layer was prepared from 95 parts by weight of high silica glass and 5 parts by weight of silicon tetraboride containing 70% by weight of particles having a size of less than 5 μm. This glass was finely pulverized with an alumina ball mill to produce powder having a specific surface area of 0.6 to ¹ m ² / g and sieved. This glass and silicon tetraboride powder were blended for 48 hours in a polyethylene container.

The powder was weighed, diluted with distilled water at a weight ratio of 1: 3, sprayed at an air pressure of 10 ⁵ Pa (1.0 atm), and applied to the barrier layer (primer layer). Sample in air, 2
Dry at 0 ° C. for 30 minutes and at 80 ° C. for 30 minutes in oven. The emissivity agent layer was baked at 1250 ° C. for 15 minutes.

Example 2 A barrier layer was prepared according to the method described in Example 1. This barrier layer contained 98% by weight of quartz glass and 2% by weight of silicon tetraboride, with 75% by weight of particles having a size of less than 5 μm.
The powder: water ratio is 1: 2 and the air pressure is 0.8 × 10.
^{It was 5} (0.8 atm). The thickness of the obtained densified layer was 70 μm. Barrier layer 1 at 1150 ° C
Bake for 0 minutes. A radioactive layer was prepared according to the method described in Example 1.

Example 3: The emissivity agent layer contained 98% by weight of high silica glass and 8 particles having a size of less than 5 μm.
2% by weight of silicon tetraboride accounting for 0% by weight. Barrier layer (primer layer) prepared by the method described in Example 2 for the radiation layer (top coat).
And was baked at 1280 ° C. for 10 minutes. The resulting coating was subjected to thermochemical and phase stability tests and erosion resistance test in a separate air stream. After 30 cycles at 1250 ° C., the α-cristobalite content was below 0.5% by weight.

The thermochemical stability was 30 μm when evaluated by the thickness of the porous layer (the defect layer formed during the thermochemical stability test) by an electron microscope. The integrated emissivity is 0.86 and the coefficient of thermal expansion is 1.1 × 10 ⁻⁶ K ^−1.
Met. No shrinkage was observed in the coating.

[0028]

As described above, according to the present invention,
High thermal stability, high thermal shock resistance, provided on a ceramic substrate,
A high temperature coating is provided that exhibits a very stable phase and low shrinkage.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 595024766 BMI-ALL, RASIAN, INSTITUTION, OF, AVITION, MATERIALS VIAM-ALL RUSSIAN IN STITUT OF OF VIATION MATERIALS Moscow, Radio, Street , 17 (72) Inventor Stanislav, Sergeie Witch, Soruntsev Moscow, Russia, Plouezd, Napolny, D, 6, Kabe, 80 (72) Inventor Vladimir, Mikhailovich, Turin Russian Federation Moscow, Boulevard, Zub Yeezdonui, D, 2, Carve, 41 (72) Inventor Natalia, Vladimirona, Izaeva Russia Japan Moscow, Wuritza, Konstantinova, Day, 9, Kavey, 60 (72) Inventor Alexei, Yuriewich, Bersenev Russian Federation Moscow, Volchaya, Ochakovskaya, Wuritza, Day, 17, Kaber, 35 (72) Inventor Galena, Anatolie Una, Solobiewa Russian Federation Moscow, Woolitza, Huatskaya, Day 1, Carve, 73

Claims (8)

[Claims] 1. A high temperature coating on a ceramic substrate, in particular a porous ceramic substrate, which coating has a silica glass and SiB ₄ content of 96.
A barrier (primer) layer containing more than wt% silicon tetraboride, and a radioactive agent (top coat) layer containing high silica glass and silicon tetraboride having a SiB ₄ content of more than 96 wt%. A two-layer high-temperature coating, characterized in that these layers, in% by weight, have the following composition: Barrier (primer) layer: Silicon tetraboride (SiB ₄ content: more than 96% by weight): 0.1 to 10%; Quartz glass: 90 to 99.9%; Emissivity agent (top coat) layer: 4 Silicon boride (SiB ₄ content: more than 96% by weight): 1.5 to 5.0% High silica glass: 95 to 98.5%. 2. The barrier layer is densified, the thickness is 70 to 140 μm, and the density is high.
The coating according to claim 1, which is 5 g / cm ³ . 3. A method for forming a ceramic substrate, in particular a porous ceramic substrate, having a coating according to claim 1, which method comprises: silicon tetraboride (SiB ₄ content> 96% by weight). )
0.1-10 wt% and quartz glass 90-99.9 wt%
Preparing a first slurry in which a powder consisting of (1) is added to a miscible dispersion medium, preferably distilled water, at a powder: liquid weight ratio of 1: 1 to 1: 5; Applying by pressure spraying onto the coated ceramic substrate, and drying the layer thus obtained, which is 1100-11
A step of obtaining a barrier layer by baking at a temperature of 50 ° C. for 10 to 20 minutes, and silicon tetraboride (SiB ₄ content exceeds 96% by weight)
1.5 to 5.0% by weight and high silica glass 95 to 98.5
And a step of preparing a second slurry in which a powder consisting of 10% by weight of a powder is added to a miscible dispersion medium, preferably distilled water, at a powder: liquid weight ratio of 1: 1 to 1: 5, Applying by pressure spraying to the barrier layer formed in 1. and drying the layer thus obtained, which is 1250-13
And a step of firing at a temperature of 00 ° C. for 10 to 20 minutes to obtain a radiation-stimulating agent layer, and a method of forming a two-layer high-temperature coating. 4. The ceramic base material is Al ₂ O ₃ , Zr.
It contains one or more compounds selected from the group consisting of O ₂ , SiO ₂ , SiC and Si ₃ N ₄ , and has a density of 0.
Method according to claim 3, characterized in that it is above 1 g / cm ³ . 5. The content of silicon tetraboride particles having a size of less than 5 μm is 70 to 80% by weight of the silicon tetraboride.
The method according to claim 3 or 4, wherein 6. The SiO ₂ content of quartz glass is 99.96.
The method according to any one of claims 3 to 5, wherein the method is wt%. 7. The method according to claim 3, wherein the high silica glass has the following composition in% by weight. _{SiO 2: 94~96% B 2 O} 3: 3.5
_{~6% Al 2 O 3: 0.1~0.5} % Na 2 O: 0.
1-0.5%. 8. A coating layer having an air pressure of 0.8 × 10 ⁵
The method according to any one of claims 3 to 7, wherein the method is applied at ˜1.1 × 10 ⁵ Pa.